1. Field of the Invention
This invention relates generally to systems for exciting a string of light-emitting diodes (LEDs), and more particularly to systems which excite multiple LED strings.
2. Description of the Related Art
LEDs are increasingly used for the purpose of providing illumination. For example, displays made from an array of liquid crystal devices (LCDs) require backlighting. This backlighting may be provided with multiple ‘strings’ of LEDs, with each string consisting of a number of LEDs connected in series.
Conventionally, LCD display backlighting is provided by exciting all of the LED strings simultaneously. Typically, the currents conducted by the strings are pulse-width modulated with a common waveform provided by an external circuit which adjusts the duty ratio as needed to obtain a desired intensity.
However, when so arranged, it is difficult to control the intensity of the light produced by individual strings, or to determine the locations of open or short circuit conditions that may exist within an individual string.